Sea-floor Spreading

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Vocabulary

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Sonar: device that uses the echoes of sound waves
Sea-floor Spreading:the process that puts old rocks to the side and new ones in the middle.
Molten Material: hot rock that erupts for the process of sea-floor spreading.
Magnetic Strips: different patterns of magnets forming the earth's magnetic field.
Drilling Samples: drilling in the ground to prove sea-floor spreading's existence.
Deep Ocean Trenches: deep under-water canyons.
Subduction: the ocean floor sinking to the mantle.

Outline

• Intro

  • Wegener's theory might be correct from evidence of sea-floor spreading.
    • "adding new material to ocean floor is called sea-floor spreading."Harry Hess said.

• Evidence of Sea-Floor Spreading

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Evidence from Molten Material

• cracked rocks on the ocean floor.
  • rocks shaped weirdly
    • rocks erupting through Central Valley of the Ocean Ridge.

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Evidence from Magnetic Stripes

• Earth's Magnetic Field changed 780,000 years ago.
  • Scientist discovered unique pattern.

• Evidence from drilling samples
  • tested how old rocks were
    • noticed how all rocks on the side are older and rocks in the middle are much younger.

• Subduction at deep-ocean trenches

  • ocean floor gets wider caused by sea-floor spreading
    • deep ocean trenches allows subduction to take place

• Subduction and Earth's Oceans

  • ocean floor completely changes outcome every 200 million years.
    • old rocks move across oceans to sink into trenches.

• Subduction in the Pacific Ocean

  • Pacific Ocean has many trenches, so the trenches swallow the Pacific Ocean parts, and the ridge is not adding new ridges fast enough.

Subduction in the Atlantic Ocean

• Atlantic Ocean is expanding because it has very few trenches
  • the spreading ocean floor has nowhere to go, so it just goes everywhere
    • the Atlantic Ocean is also sort of dragging the edges of the continents

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